Cut-away model for dental prosthesis

ABSTRACT

A model for a dental prosthesis is formed as a segment of a casting which is severed from the body of that casting by lateral cuts and by a plate imbedded in the casting. The plate, defining a parting surface between the body of the casting and the segmented model, has a noncircular pedestal which positively orients the model with reference to the body and forms a socket for a dowel serving for the temporary retention of the model on the body.

United States Patent 1191 Eberhard Mar. 26, 1974 CUT-AWAY MODEL FOR DENTAL PROSTHESIS [76] Inventor: Peter Eberhard, Georg Beutler-Str.

37, 792 Heidenheim, Germany [22} Filed: Oct. 16, 1972 [21] Appl. No.: 298,016

[30} Foreign Application Priority Data Oct. 16, 1971 Germany .J 2151671 [52] US. Cl. 32/11, 32/71 [51] Int. Cl. A6lc 13/00 [58] Field of Search 32/71, 4O, 11

[56] References Cited UNITED STATES PATENTS 3,470,6l4 10/1969 Kelly 32/11 3,553,839 l/l97l Gores 32/ll Primary ExaminerAntonio F. Guida Assistant Examiner-J. Q. Lever Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT A model for a dental prosthesis is formed as a segment of a casting which is severed from the body of that casting'by lateral cuts and by a plate imbedded in the casting. The plate, defining a parting surface between the body of the casting and the segmented model, has a noncircular pedestal which positively orients the model with reference to the body and forms a socket for a dowel serving for the temporary retention of the model on the body.

6 Claims, 5 Drawing Figures PATENTEDHARZS m4 SHEET 1 OF 2 FIG. 2

PAIENTEUMARZS Ian I 3798772 sum 2 or 2 l CUT-AWAY MODEL FOR DENTAL PROSTHESIS FIELD OF THE INVENTION My present invention relates to a dental structure of the type wherein one or moresegments of a casting, formed as a replica of the gums and denture of the patient, are cut away from the body of the casting to serve as models for individual teeth or other parts of the denture which are to be fitted with dental prostheses such as bridges or crowns.

BACKGROUND OF THE INVENTION In order to facilitate the detachment of the cut-away segment from the remainder of the casting, it has heretofore been the practice to cast the body of the structure in a mold representing an impression of the patients original dentures (i.e. gums, natural teeth and prior prostheses, if any), the mold being filled in a first casting phase only to the level of the intended parting surface between the segmental model or models and their base. After this first casting has set, the remainder of the structureis cast thereon ina manner enabling ready separation of the segmental model or models from the base. This can be done by coating the casting base with a thin partinglayer or by choosing dissimilar materials for the two casting operations, i.e. materials which upon hardening do not firmly adhere to each other. In order to hold the segmental models in position after they have been severed from the remainder of the casting, it is customary to imbed dowels or pins in the first cast and to let them project above the parting surface into the second cast; when the segment is severed, by means of lateral cuts penetrating to the contact surface of the two casts, the segment can be pulled off its base together with its retaining pin or without same. If the pin remains in the base, a hole is left in the segment which receives the projecting part of the pin when the segment is redeposited on the base. If the pin remains with the segment, a similar hole is left in the base.

In either instance, therefore, the segment can be returned to its original position after having been worked on by the technician, e.g. for the purpose of being capped. Frequent removals and reinsertions, however, tend to loosen the fit between the pin and its hole so that the structure may not maintain its original shape even if a filler is placed in the hole for better retention.'

With a single retaining pin, which in many cases is all that can be accommodated, the segment may also turn about the pin (within the limits of mobility afforded by the lateral cuts) inasmuch as such rotation is not impeded by the relative smooth parting surface which corresponds to the free surface of the molten mass poured into the mold in the first casting phase. Difficulties are also experienced in temporarily supporting the pin or pins in the mold, prior to and during this first phase, in a manner designed to hold them at right angles to the parting surface (i.e. vertical) so as to facilitate the subsequent removal and reinsertion of theassociated segments.

OBJECTS OF THE INVENTION The general object of my present invention is to provide an improved dental structure of the character set forth which insures the accurate repositioning of one or more cut-away segments even after repeated removals and re-emplacements.

A related object is to provide a process for making such a structure with avoidance of the difficulties referred to.

It is also an object of my invention to provide a structure of this type which can be cast in a single operation, i.e. without waiting for one portion of the cast to set,

.from either identical or different materials so as to afford greater flexibility in the choice of the compositions for the base and the cut-away segments.

SUMMARY OF THE INVENTION The foregoing objects are realized,.pursuant to the present invention, by imbedding one or more plates (one for each segmental model) into the casting in a position in which a surface of a plate coincides with the parting surface between the body of the casting and the segment to be cut therefrom. The plate, which is firmly anchored to the body of the casting, is detachably engaged by fastening means such as a retaining dowel partly imbedded in a segment so as to be withdrawable therewith from the body of the casting.

Advantageously, the retaining dowel used as the detachable fastening means tapers from a larger diameter in the segment to a smaller diameter in the casting body into which this dowel projects through a similarly tapering socket formed by the plate. This socket advantageously forms part of a pedestal of noncircular outline which is integral with the plate and is received in a complementary recess of the segment (formed automatically during casting) so as to hold same against rotation; in this way, the segment is positively oriented with reference to its base.

While adhesion alone may suffice to anchor the plate to the casting body, I prefer to enhance the bond between that body and the plate by forming the latter with beveled edges imbedded in adjoining portions of the casting and/or by providing bosses alongside the socket which project into the base portion of the casting body.

Advantageously, the imbedded plate consists of a synthetic resin (e.g. Teflon) which adheres only weakly or not at all to themass of the casting, especially to the composition (e.g. plaster) used for the cut-away segment. If desired, however, the surface of the plate confronting the segment could be specially treated (eg Teflon-coated) to minimize adhesion.

BRIEF DESCRIPTION OF THE DRAWING scale) of the structure of FIG. 1 (in inverted position) and the mold in which it is cast;

FIG. 3 is a bottom view of a plate imbedded in the structure, as seen on the line III III of FIG. 2;

FIG. 4 is a cross-sectional view of the plate taken on i the line IV IV of FIG. 3, with part of the surrounding casting indicated in phantom lines; and

FIG. 5 is'a cross-sectional view of the casting without the mold, after trimming and inverted with reference to FIG. 2.

SPECIFIC DESCRIPTION In FIG. 1 I have shown a dental structure 1 formed as a unitary casting of a material such as plaster conventionally used for this purpose. Separated by lateral saw cuts 5 from the body of the casting 1 are two segments 4 to be used as models for a pair of teeth to be interconnected by a bridge. The cut-away segments 4 rest on respective plates 6 (only one being visible) which are partly imbedded in the casting body and whose exposed upper faces are the parting surfaces 3 between the body and the segments 4.

As shown in FIG. 2, the structure 1 forms a base la separated by the imbedded plate 6 from the segment 4 which is cast integrally with the remainder of the structure, including the base 1a, in a mold constituted by a cup and a wax impression 14. The plate 6, resting on opposite lips 16 of the wax impression, is initially held in position by pegs 17 passing into the wax through holes 18 of the plate (see also FIG. 3). An oblong pedestal 13, integral with plate 6, is traversed by a frustoconical bore 7 which extends into a collar 9 on the opposite'side of the plate and forms with it a socket in which an upwardly tapering dowel 2 is frictionally retained during casting. Dowel 2 has a knurled extension 8 improving its bond to the segment 4 which is cast around the pedestal and the lower part-of the dowel as viewed in FIG. 2. The upstanding socket portion is flanked by bosses 11 which, along with collar 9, penetrate into the base portion 1a of the casting. The lateral edges 12 of the rectangular plate 6, extending parallel to the pedestal 13, are beveled (as best seen in FIG. 4) so as to be overlain by portions of the casting l. The entire body 1 with its segments 4 is cast in a single operation, with simultaneous hardening of all its parts.

After the casting has set, its contours may be trimmed as indicated at 1b (dot-dash lines) in FIG. 2. The resulting structure has been illustrated in FIG. 5 which also shows that the ends of plate 6 have been cut off in the trimming process. The pegs 17 of FIG. 2,

which are no longer required at this stage, may or may not be left in place.

The exposed surface of pedestal 13 is a portion of the parting surface 3 between base la and segment 4. Upon removal of the segment, the latter exposes a recess 4a which is complementary to the pedestal l3 and precisely orients the segment with reference to base la and plate 6 upon subsequent reassembly.

I claim:

1. A dental structure comprising a casting in the shape of at least a partial denture and at least one segment severed from the body of said casting by lateral cuts, said segment being a model of part of the denture; a plate provided with a throughgoing socket and imbedded in said casting between said body and said segment, said plate being anchored to said body and defining a parting surface between the latter and said segment; and a dowel anchored at one end in said segment and having its other end detachably received in said socket for temporarily retaining said segment in said casting.

2. A dental structure as defined in claim 1 wherein said dowel projects through said socket into said body said plate is provided with bosses alongside said socket projecting into said body for holding said plate in position thereon.

5. A dental structure as defined in claim 1 wherein said plate has beveled edges imbedded in adjoining portions of said body.

6. A dental structure as defined in claim 1 wherein said plate consists of synthetic resin. 

1. A dental structure comprising a casting in the shape of at least a partial denture and at least one segment severed from the body of said casting by lateral cuts, said segment being a model of part of the denture; a plate provided with a throughgoing socket and imbedded in said casting between said body and said segment, said plate being anchored to said body and defining a parting surface between the latter and said segment; and a dowel anchored at one end in said segment and having its other end detachably received in said socket for temporarily retaining said segment in said casting.
 2. A dental structure as defined in claim 1 wherein said dowel projects through said socket into said body and tapers from a larger diameter at said one end to a smaller diameter at said other end.
 3. A dental structure as defined in claim 1 wherein said socket is part of a pedestal of noncircular outline integral with said plate and received in a complementary recess of said segment for orienting same with reference to said body.
 4. A dental structure as defined in claim 1 wherein said plate is provided with bosses alongside said socket projecting into said body for holding said plate in position thereon.
 5. A dental structure as defined in claim 1 wherein said plate has beveled edges imbedded in adjoining portions of said body.
 6. A dental structure as defined in claim 1 wherein said plate consists of synthetic resin. 